WooCommerce - Add custom post_meta data to the order REST API response.

functions.php

<?php
	
	/**
	 * Hook into order API response to add custom field data.
	 *
	 * @param $order_data   array
	 * @param $order   		WC_Order
	 * @param $fields   	array
	 * @param $server   	array
	 *
	 * @return $order_data	array
	 */
	add_filter( 'woocommerce_api_order_response', 'add_foo_field_order_api_response', 20, 4 );
	function add_foo_field_order_api_response( $order_data, $order, $fields, $server ) {
		
		// Get the custom order post_meta data and add it to the order_data array.
		$order_data['foo'] = get_post_meta( $order->id, 'foo', true );
        
		return $order_data;
	}
    

Notes:

https://stackoverflow.com/questions/36369388/woocommerce-rest-api-custom-fields
https://stackoverflow.com/questions/39019579/custom-value-in-woocommerce-webhook-payload
https://stackoverflow.com/questions/40802219/woocommerce-rest-api-extending-order-response

Can we add BillingId: xxx (where xxx is the parent company id) to the CIN7 customer details so that all web store invoices get associated with the one Xero contact?

No idea if CIN7's delivery URL will actually receive BillingId but worth exploring

Thaaanks